This invention relates to pneumatic springs which are utilized in lieu of mechanical springs for absorbing the force of movement of two bodies as can occur in use to cushion the movement of one die with respect to another as in the clamping of a workpiece in a press for forming sheet metal parts. Typical prior art of pneumatic springs of this type are shown in the U.S. Pat. Nos. 3,101,194, 3,281,138, and 3,379,430.
Among the objectives of the present invention are to provide a pneumatic spring which will effectively cushion the forces; which provides two cushioning chambers which are independent of one another; and which includes chambers that will function independently of one another so that if there is leakage with respect to one chamber, the cushioning action of the other chamber will not be affected and which is easily maintained.
In accordance with the invention, the pneumatic spring comprises an outer housing defining an open-ended outer cylinder, and an inner cylinder slidingly and sealingly positioned in the outer cylinder. The inner cylinder has a cylindrical side wall and end walls. A rod extends from the inner end wall of the outer cylinder, and a piston is fixed on the rod within the inner cylinder, thereby defining a first chamber between the inner end of the outer cylinder and the inner end wall on the inner cylinder and a second chamber between the piston on the rod and the outer end wall of the inner cylinder. The chambers are isolated from one another, and valve means provide gaseous fluid under pressure to each of the chambers independently of the other whereby when a force is applied to move the inner cylinder axially inwardly of the outer cylinder, the pressures on the two chambers are built up independently of one another. In another form, the pneumatic spring comprises an open-ended outer cylinder and an open-ended inner cylinder slidingly and sealingly positioned within the outer cylinder with the valves in the end wall of the outer cylinder.